In the existing CMOS image sensor, discrepancy in the threshold value of MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) used for a pixel cell circuit may generate fixed-pattern noise (FPN) on a picked-up image.
In recent years, methods of suppressing such discrepancy in the threshold value have been conceived (e.g., see Patent Documents 1 to 6 and Non-Patent Document 1). In these methods, the voltage of a floating diffusion (FD) is controlled for each pixel by negative feedback so that the pixel output is kept constant.    Patent Document 1: Japanese Patent Application Laid-open No. 2005-110275    Patent Document 2: Japanese Patent Application Laid-open No. 2012-19167    Patent Document 3: Japanese Patent Application Laid-open No. 2012-19168    Patent Document 4: Japanese Patent Application Laid-open No. 2012-114838    Patent Document 5: Japanese Patent Application Laid-open No. 2012-151369    Patent Document 6: Japanese Patent Application Laid-open No. 1998-281870    Non-Patent Document 1: Non-Patent Document 1: Ryo Kagaya, Masayuki Ikebe, Tetsuya Asai, and Yoshihito Amemiya, “On-Chip Fixed-Pattern-Noise Canceling by Negative-Feedback Reset for CMOS Image Sensors,” The Journal of The Institute of Image Information and Television Engineers, VOL. 59, No. 3(2005), Hokkaido University, 2005